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NAG[g05ecc] NAG[nag_ref_vec_poisson] - Set up reference vector for generating pseudo-random integers, Poisson distribution
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Calling Sequence
g05ecc(t, r, 'fail'=fail)
nag_ref_vec_poisson(. . .)
Parameters
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t - float;
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On entry: the mean,  , of the distribution.
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Constraint:  . .
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r - assignable;
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Note: On exit the variable r will have a value of type float.
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On exit: reference vector for which memory will be allocated internally. If no memory is allocated to r (e.g. when an input error is detected) then r will be NULL on return, otherwise the user should use the NAG macro NAG_FREE to free the storage allocated by r when it is no longer of use.
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'fail'=fail - table; (optional)
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The NAG error argument, see the documentation for NagError.
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Description
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Purpose
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nag_ref_vec_poisson (g05ecc) sets up the reference vector r for a Poisson distribution with mean  .
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Description
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This sets up a reference vector for use in g05eyc (nag_return_discrete). Together these functions produce random numbers from the Poisson distribution defined by:
![[[P(I,=,i)=(t^ie^(-t))/(i!) , i=0,1,..],[P(I,=,i)=0, ]]](/support/helpjp/helpview.aspx?si=9907/file08476/math76.png)
The reference array is found using a recurrence relation if  is less than 50 and by Stirling's formula otherwise.
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Error Indicators and Warnings
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"NE_ALLOC_FAIL"
Dynamic memory allocation failed.
"NE_REAL_ARG_LT"
On entry, t must not be less than 0.0:  .
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Examples
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>
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t := 2.7:
NAG:-g05cbc(0):
NAG:-g05ecc(t, r):
x := Vector(5):
for i from 1 to 5 do
x[i] := NAG:-g05eyc(r):
end do:
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